The present invention pertains to well constructions and methods of inhibiting microbial growth in wells.
The presence of microbial growth can cause bio-fouling and plugging of wells. Such plugging can occur both in vadose-zone wells and in saturated-zone wells. Vadose-zone wells are wells having a well bore that does not extend into the water table, and include, for example, vadose-zone monitoring wells, vapor extraction wells and injection wells. Saturated-zone wells have a well bore that extends into the water table such as, for example, ground water monitoring wells, production wells and irrigation wells. Plugging of a well may occur by plugging of structures within the well such as the filter pack, screening, piping, or pumps. Plugging may also occur by the plugging of the surrounding geological media Such plugging is caused by an accumulation of microbial growth, by an accumulation of microbial extracellular material, or both.
Once a well has become bio-fouled or plugged, treatment of the well to eliminate microbial growth and remove plugging is often difficult and ineffective. Remedial chemical treatments, such as an introduction of a highly concentrated chlorine solution into the well, often fail due to the difficulty in forcing the solution through an already plugged well. Once bio-fouling has occurred, replacement of the effected structure is often required. Severe bio-fouling and plugging may require replacement of the entire well at great expense.
Accordingly, it is desirable to provide well constructions and preventative treatment methods designed to minimize unwanted microbial growth in wells.
In one aspect, the invention encompasses a method of inhibiting microbial growth in a well. A well bore is provided. A first material is mixed with an antimicrobial agent to form a packing material. The packing material is used to fill at least a portion of the well bore.
In another aspect, the invention encompasses a material for packing within a well. The material for packing the well includes either sand or gravel, or both. The material for packing the well also includes an antimicrobial agent. The antimicrobial agent can be in powdered form, in granular form, in pellet form, in tablet form, in precipitate form, or can be a mixture of two or more of these forms.
In another aspect, the invention encompasses an additional method of inhibiting microbial growth in a well. A well bore is provided that has a depth extending from a ground surface. A casing is provided within the well bore and is at least partially surrounded by an annular space. One or more access tubes are provided within the annular space of the well bore, outside the casing. The access tubes have a first terminal opening located at or above the ground surface and have a length that extends from the first terminal opening at least part of the depth of the well bore. The access tubes have a second terminal opening located within the well bore. An antimicrobial material is supplied into the well bore through the first terminal opening of the access tubes.
In still another aspect, the invention encompasses a well construction having inhibited microbial growth. The well construction includes a well bore and a well casing within the well bore. The casing has a terminal end within the well bore and has a screened portion that extends from the terminal end to a first elevation within the well bore. Multiple access tubes encircle the casing within the well bore. The access tubes have a terminal end within the bore and have a perforated segment extending from the terminal end to a second elevation within the well bore. The well bore contains a layer of packing material comprising a first antimicrobial agent mixed with either sand or gravel, or mixed with both sand and gravel. The layer of packing material fills the well bore to a third elevation. The well construction includes a second antimicrobial agent which, when provided through an access tube, is able to pass from within an access tube into the packing material through the perforated segment of the access tube.